1. Field of the Invention
The present invention generally relates to a PHS terminal device and a method of receiving PHS data. More specifically, the present invention relates to a PHS terminal device and a method of receiving PHS data, especially, a PHS terminal device, which receives PHS data that are made having a time slot including a Unique Word, and a method of receiving the PHS data.
2. Background Information
PHS (Personal Handyphone System) is called a second generation cordless telecommunication system. The Association of Radio Industries and Businesses (ARIB) defines the standard of the communication method of PHS. The standard is called the ARIB STANDARD and an example of the standard is RCR STD-28 V4.0. According to the standard, a PHS terminal device searches for a base station right after the PHS terminal device is activated. At that time, the PHS terminal device detects a control signal that a base station periodically emits. The control signal that the base station periodically emits contains data called a Unique Word (UW), and the PHS terminal device recognizes that it could find a base station if it detects a Unique Word in a control signal. To the contrary, if the PHS terminal device cannot detect a Unique Word, it recognizes that base stations are outside the communication range and periodically repeats a search for a base station. Related Examples of a conventional PHS terminal device are described in Japanese Patent Publications JP-A-6-315025 and JP-A-8-186473, which are hereby incorporated by reference.
Japanese Patent Publication JP-A-315025 (especially, page 4 and FIG. 1) discloses a PHS terminal device that is made of a reception data shift resister, a Unique Word detecting circuit, a slot counter circuit, and a timing control circuit. The reception data shift register outputs data of a bit position corresponding to the Unique Word to the Unique Word detecting circuit. The Unique Word detecting circuit receives data output from the reception data shift resister in real time, and outputs a corresponding signal if the received data correspond to a pattern of a Unique Word. The slot counter circuit establishes a slot synchronization by setting the initial value according to the corresponding signal, and reports establishment of the slot synchronization to the timing control circuit. The timing control circuit controls a timing of the whole receiving process in response to the report of the establishment of the slot synchronization. In addition, the Unique Word detecting circuit outputs the corresponding signal as a reception completed signal to a CPU.
Japanese Patent Publication JP-A-8-186473 (especially, page 3-4, FIGS. 1 and 5) discloses a PHS terminal device that is made of a local oscillator, a mixer, a demodulator, an error correction demodulator, a demodulator synchronization detecting circuit, a Unique Word detecting circuit, a carrier wave ID detecting comparator, and a local oscillator sweeping control circuit. The local oscillator sweeping control circuit sweeps frequencies of the local oscillator from an initial value. The mixer converts the reception data to an intermediate frequency signal. The demodulator demodulates the intermediate frequency signal. The error correction demodulator executes an error correction demodulation for the signal from the demodulator. The demodulator synchronization detecting circuit receives the signal from the modulator, and detects whether synchronization between a carrier wave and bit timing is established. The Unique Word detecting circuit receives the signal from the demodulator, and detects whether a Unique Word is detected. The carrier wave ID detecting comparator detects whether a carrier wave ID corresponds to a predefined carrier wave ID. The PHS terminal device executes a frame synchronization process only when a Unique Word is detected and a carrier wave ID corresponds to a predefined carrier wave ID after the synchronization between a carrier wave and a bit timing is established.
Downsizing and low-consumption technologies of a PHS terminal device have been developed recently. These types of technologies have also been developed for a baseband LSI for PHS terminal device functions in a battery saving mode. In the battery saving mode, for example, a PHS terminal device executes intermittent reception that stops the clock of a CPU while it does not receive data and lowers power consumption. However, it is difficult to output a reception reference signal correctly in the battery saving mode because the clock of the CPU is stopped between outputs of reception reference signals. Therefore, a Unique Word (UW) detecting signal is used as a synchronization signal in the battery saving mode. In a case that a UW detecting signal is used as a synchronization signal, a UW detecting indication bit is activated in synchronization with a UW detecting signal when a UW detecting signal is output in receiving reception data. Further, a UW detecting indication bit is reset in synchronization with a rising edge of a reception completion detection indication bit, and then a reception completion interrupting signal is output. In this case, there is a problem in that the check result of whether a UW detecting signal is detected cannot be confirmed because a UW detecting indication bit has already been reset in a reception completion interrupting routine started in response to a reception interrupting signal. However, in the patent publications described above, there is no description of the problem of a Unique Word being undetectable in the battery saving mode.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved PHS terminal device and a method of receiving PHS data. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.